<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <link rel="stylesheet" href="./demo02.css">
    <style>
        /* .ha li{
            color:blue;
        } */

        a{
            color:red;
        }

        a:hover{
            color:blue;
        }

        a:active{
            color:green;
        }
    </style>
</head>
<body>
    <p class="first">hello world</p>
    <p class="second">hello world</p>
    <p class="third fourth">hello world</p>
    <p id="haha">hello world</p>
    <ol class="ha">
        <li>haha</li>
        <li>haha</li>
        <li><a href="#">这个</a></li>
    </ol>
</body>
</html>